In the last few decades, the production of polymers and plastics has been increasing rapidly. Among polymers, those that are processable into shapes such as films, fibers, and other objects have been in much commercial demand for various applications. Recent years have seen an increase in demand for polymers which have high temperature stability so that they can be processed at high temperatures with no degradation or chemical change, and the finished products may be used in high temperature applications such as, for example, those that are encountered in the electronics and aerospace industries.
Several uses for polymers are in outdoor applications where they are subjected to actions by light, heat, atmospheric oxygen and other environmental agents. Weathering conditions have always been an important problem in such applications. Ultraviolet radiation is especially a problem since it can not only cause degradation in the polymer on its own, but also cause a chemical change in the polymer which may consequently become vulnerable to attack by other environmental conditions. Thus, protection of polymers from ultraviolet radiation has been of interest for many years. A description of techniques to protect polymers from ultraviolet radiation is provided by J. F. Rabek, Photostabilization of Polymers-Principles and Applications, Elsevier Applied Science, New York, 1990.
Many approaches have been taken in the past to protect polymers from ultraviolet (uv) radiation. Generally, small molecules that are good uv absorbers are used as additives in the formulation. During the exposure, these additives absorb the uv radiation preferentially, thus preventing the radiation from reaching the polymer. For example, the Uvinul.TM. materials (from BASF Corporation, Chemicals Division, Parsippany, N.J.) and the Tinuvin.TM. additives (from Ciba Geigy Corporation, Additives Department, Hawthorne, N.Y.) are uv stabilizers that are commercially available for use with polymers. Such materials, however, have problems with thermal stability. Recently, several new polymers have come on the market which need to be or can be processed at high temperatures, for example, above 300.degree. C. When additives such as those mentioned above are used as uv stabilizers (alternately referred to as photostabilizers) with such high temperature polymers which are then processed at high temperatures, the additives either thermally decompose or sublime away, leaving the polymer with no uv protection.
Polymeric stabilizers have been proposed to overcome this thermal instability problem. In such materials, the additive uv absorbing moieties are bound to polymer backbones. Photostabilization of Polymers, referred to above, describes several polymer-bound additives on pages 202-278. Polymer-bound stabilizers generally are used as additives to the polymers which are to be protected. These materials also have drawbacks. Some of them, even as part of polymer, may still be inherently thermally unstable. Another drawback is that depending on their molecular weights, some polymers may be limited in the amounts that can be added. They may also not stay as a homogeneously distributed part of the final product. Compatibility with the polymer to be protected may be yet another drawback.
Thus, there is a need for materials which can function as uv stabilizing agents that are stable under high temperature process conditions. It will be desirable if they can not only be used as blended additives to the polymer to be protected, but also as materials that can be incorporated into the backbone of the polymer that is to be protected. When incorporated into the backbone, the protecting moieties may stay as an integral, compatible part of the product at desired concentrations.
Accordingly, it is an object of this invention to provide oligomeric uv stabilizers that possess high thermal stability.
It is another object of this invention to provide oligomeric uv stabilizers that possess reactive functionalities so they may be incorporated into the backbone of polymers.
It is a further object of this invention to provide oligomeric uv stabilizers which can be used as compatible blended additives for polymers.
It is yet another objective of this invention to provide oligomeric uv stabilizers that possess high enough thermal stabilities to withstand high temperature processing of polymers to which they are added or in which they are incorporated in the backbone, so that the resulting finished product retains uv stability.
These and other objects of the present invention will become apparent to the skilled artisan upon a review of the following specification, and claims.